Once inside Roman's taxi, you'll be introduced to the driving mechanics. The minimap in the bottom-left corner of your screen will display a yellow GPS route. Follow this route to Roman's apartment in Broker. Use the W key to accelerate, S to brake/reverse, and A/D to steer (PC controls).
The drive is straightforward and serves as a gentle introduction to Liberty City's traffic. Roman will continue to talk during the drive, providing more exposition about his life and the city. Don't worry about driving perfectly; the mission is forgiving. Just focus on following the GPS and getting a feel for the vehicle controls. Upon reaching the apartment, another cutscene will trigger, concluding the mission.